Penguins are a remarkable group of flightless birds. We tend to think of them as Antarctic birds, but they actually inhabit an extremely diverse range of habitats from subzero Antarctic coastline to the tropical Galapagos Islands. Research we published today in the Biology Letters gives us new insight into how this diverse group evolved.
There are now 18 recognised species of penguins. All live predominantly in the Southern Hemisphere (those Galapagos penguins being the exception), in a wide range of climates.
The habitats of modern penguins can be grouped into four climate zones. The Galapagos penguin (Spheniscus mendiculus) lives in a tropical habitat and two other species, the Peruvian penguin (S. humbolti) and the Black–footed (S. demersus) live in the subtropical regions.
Meanwhile Adélie, Chinstrap and Gentoo species (belonging to the genus Pygoscelis), the King and Emperor penguins (genus Aptenodytes) and Macaroni and Rockhopper penguins (both species of Eudyptes) are classic polar penguins, living in the Antarctic and sub-Antarctic.
The remaining eight species of penguins — the Fiordland, Snares, Erect-crested, Royal, Yellow-eyed, Magellanic, White-flippered and Little Blue penguin — live in temperate regions of the world.
Where penguins live can tell us something about how they are related. We can also look at fossils. Fossil penguins have been recovered from a range of latitudes in the Southern Hemisphere — from New Zealand to Peru. The earliest penguin-like fossil is 59-61 million years old, but fossils related to living penguins are very recent, less than 10 million years.
We assume that all living penguins are descended from one species. To find out when that species lived, we can look at similarities of body shape (morphology) between fossils and living species. Using this morphological method previous studies estimated quite a young age for the ancestor of all living penguins, between 15 and 20 million years ago.
Another method is to use DNA sequences extracted from blood samples of living penguins. Previous studies using this molecular method gave ages much older than those based on morphological data.
Morphological and molecular methods have different limitations and uncertainties. That means to determine the actual age of the penguin ancestor, we need to use both.
Our study published today gives a result that brings morphological and DNA evidence together.
We obtained blood samples from 11 penguin species belonging to all six groups (genera) of penguins living in four distinct climates. We then extracted DNA sequences from these samples through standard molecular biological techniques. We analysed the sequences using computational methods to examine how different penguins are related. Finally we used sophisticated analytical software to precisely estimate the age of the penguins’ ancestor. Our analysis suggests the ancestor of all modern penguins lived 20 million years ago, much younger than previous molecular studies.
Our analysis also showed that the major penguin lineages diverged around 10-15 million years ago. What can this tell us about penguin evolution?
Interestingly Antarctica saw rapid cooling around the same time — 10-15 million years ago. At this time Antarctica developed a permanent ice cap that covered the entire continent. We connected these two dots and speculate that there might be connection between the rapid cooling of the Antarctic and the divergence of the penguin lineages.
Although we don’t have any proof for this connection, it’s a fascinating idea that adds to what we know about evolution and how past climate change has affected species.